1. Field of the Invention
This invention relates to a driving power transmission system for transmitting the driving power of a driving electric motor, such as a reel motor, adapted for rotationally driving a rotationally driven unit, such as a reel block unit of a tape recorder, to the rotationally driven unit.
2. Description of the Prior Art
There has previously been employed a reel block driving unit in a tape recorder in which a driving electric motor used exclusively for driving a pair of reel blocks is provided between the reel blocks and in which these reel blocks are selectively driven in rotation by the driving electric motor as a function of the selected magnetic tape running mode.
The reel block driving unit is provided with a driving power transmission switching system in which a lever having a pivot on a driving shaft of the driving motor is provided and an idler gear selectively meshing with rotary gears of the reel blocks is provided on the lever. The driving power transmission switching system is so constructed that the aforementioned lever is rotated by means of a friction unit in dependence upon whether the driving motor is rotated in forward or in reverse, with the idler gear on the lever meshing with one of said rotary gears for selectively driving one or the other of said reel blocks in rotation.
The above described reel block driving device is adapted for directly transmitting the driving power of the driving motor to the rotary gears of the reel blocks by means of the driving power transmission gears, such as idler gear. The result is that disturbance factors disturbing the rotational driving, such as torque ripples proper to the driving motor, are directly transmitted to the rotary gears of the reel blocks. If torque ripples are transmitted to the rotary gears of the reel blocks, stable rotational driving of the reel blocks cannot be achieved to affect the tension of the magnetic tape to be wound on tape reels engaged with the reel blocks to produce wow and flutter in the running tape to render it impossible to obtain satisfactory recording/reproducing characteristics.
Thus the above described reel block driving apparatus is designed to realize a high velocity driving of the reel blocks by taking advantage of the rotational driving force of the driving motor only during the fast feed or rewind mode operations not affecting the recording/reproducing characteristics. On the other hand, when running the magnetic tape at a constant, such as during the recording/reproduction, the reel blocks are driven without resorting to the driving power of the reel block driving motor, the driving power of which is directly transmitted to the reel blocks by means of idler gears or the like. For example, a driving motor provided for driving a capstan shaft in rotation in addition to the reel block driving motor and the reel blocks are interconnected by a belt connecting system, such as a rubber belt, by means of which torque ripples of the driving motor maybe absorbed to realize satisfactory rotational driving of the reel blocks.
In the above described conventional reel block driving apparatus, the drive power transmission changeover system for transmitting the rotational driving power of the reel block driving motor to a selected one of the reel blocks as a function of the rotational direction may be simplified in structure to simplify the apparatus to contribute to size reduction of the tape recorder.
However, in the above described conventional reel block driving apparatus, torque ripples of the driving motor are directly transmitted to the rotating reel blocks to produce wow and flutter in the tape being wound by the reel blocks. For this reason, the reel block driving apparatus cannot be used during the recording/reproducing mode in which the tape is run at a constant velocity, so that it becomes necessary to provide a separate driving system for the reel blocks, which renders it impossible to simplify the system satisfactorily.